Bob C
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| posted on 12/8/06 at 04:58 PM |
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Seatbelt upper mounting height
Like lots of folk - I now find the chassis top tube is too low and the rollbar horizontal cross brace too high to work nicely with the seatbelt holes
in my seats. I have an idea to get it right (see the dodgy paint diagram below) and was wondering
1) if anyone had seen anything like the metal clip I've drawn (ie where could I get something)
2) will mr SVA man be happy....
cheers
Bob
 
Rescued attachment sbeltclip.GIF
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JohnN
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| posted on 12/8/06 at 05:06 PM |
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Why don't you just bolt the seatbelt on the underside of the crossbar, from your diagram it looks to be the right height. Remember, the threaded
insert must be fully welded in at both ends.
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nib1980
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| posted on 12/8/06 at 05:14 PM |
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I agree with the above, I would strongly not suggest your clip idea.
I design seatbelts for an OEM and the idea you've made would scare me and most of the guys I work with. I'm only saying this to help, I
mean nothing nasty, just don't wanna see you hurt.
hope this helps
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Bob C
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| posted on 12/8/06 at 06:12 PM |
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Cheers fellers,
I should explain - I have 7/16 nuts welded to a plate welded on the top chassis bar in the time honoured tradition & the paintwork is complete -
I'd prefer not to do more welding if I can avoid it at this stage.
Why do you feel the design above would be worse than draping the belt over the bar ? (which seems not uncommon). If the crossbar acted like a friction
free pulley (which it ain't) the stress on it would be 41% higher than than bolting directly to it; but with the advantage of no holes or welds
in the crossbar at its most highly stressed points.
The clips themselves look similar to the adjusting buckles used on belts before inertia reels became popular.
any more thoughts?
cheers
Bob
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RazMan
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| posted on 12/8/06 at 06:17 PM |
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I think the whole clip & belt assembly would just rotate around the roll bar wouldn't it? In any case the radius of the clip would be a
problem IMO - it would act like a knife edge when stressed..
My harness rear mounts are low down and go up & around a horizontal bar as you describe. I had to move the seat harness holes upward to make
everything line up. It was the only answer for me
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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nib1980
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| posted on 12/8/06 at 06:34 PM |
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it would act like a knife edge when stressed..
As above, Its not so much the load as where the load is placed, running the webbing over the bar would be fine. but running it through the clip would
focus the load, and unless your getting special heat treated and coated material for this, the load will snap the clip under load. the main reason
being, a 30mph ofset frontal crash will, will see the occupant generate a minimum of 35G, and I suspect the clip will not resist that. The belts we
use in commecial cars, have specialist surfaces to run over, but all roll surfaces are designed to pull together (accutaley) not away and tear the
holder apart.
If the belt was folded over the bar and stichted (difficult in itself) it would be fine.
Hope this helps
Forgot to mention I'm assuming your refering to lap belts type systems for rear center occupants. if so these have been outlawed since the
begining of last year now in all new manufatured cars
[Edited on 12/8/06 by nib1980]
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Bob C
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| posted on 13/8/06 at 06:54 PM |
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Sorry to keep going on about this...
below is a pic of a commercially available, well respected, seatbelt end (it's a sabelt bit). It's a piece of ~3mm plate with a slot &
a hole in. That slot is subject to ~30% less stress than mine would be with the same force on the webbing, but far worse "knife" action!
Widespread use of parts like that in the picture makes me think that the "knife effect" is not real - how many people have died because
lasercut steel seatbelt hardware has sliced through the belt - I've never heard of that!!!!
I was hoping to find a commercially available slotted plate I could use - which would be rated to exceed the strength of the seatbelt webbing, and
incorporate plastic "edge blunting" bits like the ones in my tintop.
What force does a 2" seatbelt web snap at? I thought it was about 2 tons.
I've not quite ditched this notion yet.... ;^)
Bob
PS the webbing won't rotate round the crossbar unless it stretches..... I don't think seatbelts do that much ! ! !
[Edited on 13/8/06 by Bob C]
 
Rescued attachment sabelt.jpg
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RazMan
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| posted on 13/8/06 at 07:17 PM |
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Bob, how much height would you have to lose to make every thing line up exactly? From your drawing it looks as though you would only gain about 20mm
by putting the webbing through the clip as the 45 degree angle would negate some of the advantage.
I am not a belt designer and just an armchair engineer, but wouldn't the forces on the clip would be completely different on your clip (opposing
stress forces) when compared to the conventional harness end clip?
I see what you mean about the belt only rotating if it stretches though 
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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Peteff
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| posted on 13/8/06 at 09:17 PM |
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Can't you just loop it up round the crossbar and through your seat holes?
 
Rescued attachment belt loop.jpg
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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Bob C
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| posted on 14/8/06 at 11:37 AM |
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Pete - that is SO squalid..... ;^)
Razman - me too (armchair engineer) - trouble is us locost builders then go out & risk our lives in our creations......
Stresses can't be any different - it's a glorified piece of string it can only pull!!! - the clip is being pulled apart - period!
cheers
Bob
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